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Ahead to Upgrade It: CPU

Tune It

Push your PC to its limits

By David W. Methvin
Senior Technical Editor

If you're willing to roll up your sleeves, you can use Wintune's tips and advice to boost your system's performance to the max. To get started on your tune-up session, run the full range of Wintune tests on your system. Once the testing is complete, Wintune will list performance-tuning tips. You can implement Wintune's tips by checking out the sections that follow on CPU, memory, disk and video tuning. Most of these procedures apply to both Wintune 95 and Wintune 2.0, so feel free to follow along no matter which version of Windows you're using. Even if you don't have Wintune yet, the advice in this article can help you identify problems, although you may need to do a little more detective work yourself to figure out their cause. Here's an outline of the basic strategy:

As you examine results from multiple Wintune runs on your own system, or compare your system to others, remember that minor variations of 10 percent or so are insignificant. By their nature, benchmarks only approximate real-world performance. To attain performance gains that you'll really notice, work on areas that show variations of 30 percent or more.

Top Tuning the CPU Tuning the Memory Tuning the Hard Disk Tuning the Video Top Tips A Clock and Bus Story Tuning the AMD Chip

Tuning the CPU

It's one of the most prominent, expensive and heavily promoted (e.g., "Intel Inside") system parts, so the CPU is probably the first component you'll point the finger at when your system isn't running up to snuff. Certainly, the CPU makes a big contribution to overall performance. But it's also expensive to replace or upgrade. Better to try a few other tricks before running out to the store for a new processor.

The Dhrystone score is the best indicator of whether your performance problem is CPU-related. Generally, the Dhrystone results for systems running at the same clock speed are within 10 percent of one another. Compare your system's Dhrystone number to those of equivalent systems in Wintune's database. If it's significantly less, you've got a problem. Wintune will give you a tip if it sees performance that's significantly lower than it expects for your level of CPU.

How can BIOS parameters get so out of whack? You may have accidentally reset or turned off the system while it was still doing the initial power-up memory or system checks that happen right after you turn on the power. The next time you started the system, the BIOS noted that you didn't boot completely last time, and it made a last-ditch effort to get the system up and running by resetting the BIOS parameters to their most conservative (in other words, slow!) values. Some BIOS software warns you it has done this by printing a message like "Using default configuration" when you boot.

Of all the BIOS settings related to the CPU, the one for CPU internal cache-sometimes called level 1 cache-is the most important. If the CPU's internal cache is turned off, performance will be dismal. A system for diagnosing this problem using Wintune is outlined in the sidebar "Cache In, Cache Out" that's part of the Test It story. Most of the other BIOS settings relate to memory performance, so they'll be covered in this article's Memory section.

Here's a question from the "Is it plugged in" category, but we've seen it enough times that it warrants a mention. It's easy to bump those front-panel Turbo switches that many PCs have, and performance will plummet as a result. Sometimes the Turbo switch is in the right position, but isn't functioning properly. If the position of the Turbo switch doesn't seem to affect the system's speed, check its connection to the motherboard. Some motherboards default to the nonturbo (slow) settings if the switch is accidentally disconnected.

In addition, software-related issues can affect CPU performance. First up are "CPU vampires." When most Windows programs are minimized (as an icon in Windows 3.1x or on the taskbar in Windows 95), they don't use much CPU time. However, there are a few that will take up a lot of CPU time even when they're not doing anything useful. The "CPU Load" measure in Wintune 95 will tell you if you're running a CPU-vampire program. One offender is America Online 1.5; keep it closed unless you're actually connected to AOL.

With Windows 95, even a CD-ROM drive can become a CPU vampire. On some systems, and with certain CD-ROM drives, Win95's AutoPlay feature can sap CPU energy. That's because it polls the drive every second or so to see if a new CD has been inserted. If this happens with your system, leave a CD in the drive all the time. That usually solves the problem. If that doesn't help, disable AutoPlay. Run Control Panel/System/Device Manager, then select your CD-ROM drive and click on Properties. Uncheck the Auto Insert Notification option.

Now we've exhausted all the easy-to-identify (and easy-to-fix) things that might overtax the CPU. Yet no matter what you tweak, your old 486/33 isn't going to be fast. You can try a CPU upgrade as a boost for your PC's midlife crisis. Intel, AMD and Cyrix all make clock-multiplied CPUs that can fit into an old 486 motherboard, but remember that-because of hardware compatibility problems-these chips don't always work well with older systems. Make sure you get a money-back guarantee in case it doesn't work, and benchmark your system after the upgrade to see if it really helped. (See the article CPU later in this issue.)

Top Tuning the CPU Tuning the Memory Tuning the Hard Disk Tuning the Video Top Tips A Clock and Bus Story Tuning the AMD Chip

Tuning the Memory

Be realistic about memory. Don't waste time on a tune-up if you don't have at least 8MB of RAM installed in your system. This applies whether you run Windows 3.1x or Windows 95. Many of the other tips won't do you much good unless you have enough memory installed. If you're buying a system on a tight budget and have a choice between a slightly faster CPU or an upgrade to 16MB of RAM, go for the RAM. That's how important memory is to performance.

RAM compression software is not a substitute for the real thing, no matter which version of Windows you run. Some of these programs help to solve a problem Windows 3.1x has with limited DOS memory, but installing Windows 95 will do the trick, too. You're probably best served by upgrading your operating system. Third-party RAM compressors often have side effects and incompatibilities, without increasing performance. Real RAM will be useful on your PC no matter what operating system you run, and it won't become obsolete when a new Windows is released.

Nearly all Pentium systems, with the exception of some 75MHz models, have an external RAM cache. As with the CPU cache, some BIOS versions will disable the external level 2 RAM cache without telling you. The effect isn't as dramatic as when CPU cache is disabled, so it's easy to miss. However, Wintune can help you identify the situation quickly.

Once you're out of real RAM, Windows uses a swap file (Windows 95 sometimes calls it a page file) to temporarily hold memory sections that aren't immediately required. Let's say you're editing a Microsoft Word document. You minimize it, start Adobe Photoshop and create a large image. To get the memory for the image, Windows may move all or part of Word to the swap file. Now it can use Word's former space to hold your image. If you then click on Word to resume working on your document, it may swap all or part of Photoshop and your image. All versions of Windows use the same technique. Constant swapping is very time-consuming and slow, since a hard disk is 10 times slower than RAM. That's why you need plenty of RAM.

With hard disk prices coming down even as sizes increase, it's common for systems to have two hard disks. Chances are you configured the new drive as your second hard disk with drive letter D: . However, your default swap file location is probably still on your older and slower C: drive. Move the swap file to D: and you'll see a performance boost, especially if you have less than 16MB of RAM and run several applications at once. To make the switch in Windows 3.1x, set the swap file location in Control Panel/Enhanced/Virtual Memory/Change. In Win95, go to Control Panel/System/Performance/Virtual Memory.

Swap file management in Windows 95 can cause strange disk behavior. Let's say you're running Word, Photoshop and Netscape. Most likely all those programs are using a lot of memory, and your swap file on disk is relatively large, perhaps 25MB or so. At 8 p.m., it's finally time to stop working, and you close all your applications. You go to get your jacket and briefcase, then walk back to your desk to close down Windows. The disk light goes on, and the disk rattles continuously for nearly 20 seconds.

What you saw was Windows 95 doing some housekeeping. When the system is idle and Windows 95 notices that the memory demand has decreased significantly-as it did when you closed Word, Photoshop and Netscape-it will shrink and reorganize the swap file to save disk space and make future accesses to the file more efficient. If you're bothered by this, you can set the minimum swap file size to be large enough that Windows won't try to shrink it down. You can find a good minimum size to use by looking at the actual size of WIN386.SWP while you're running your typical application mix. Follow the procedure you use for setting swap file location.

You'll still occasionally see disk activity in Windows 95 that doesn't correspond to anything you've done. One explanation is that during idle times, Windows 95 likes to move changed data from memory to the swap file, thinking this may save time if the memory is needed later by some other program. It's a good general philosophy when you're short on RAM, but it can be surprising if you're not used to it.

Top Tuning the CPU Tuning the Memory Tuning the Hard Disk Tuning the Video Top Tips A Clock and Bus Story Tuning the AMD Chip

Tuning the Hard Disk

Between your own use of files and Windows' use of the swap file, the hard disk gets quite a workout. A fast hard disk is vital to performance. Fortunately, hard disk prices have been going down as performance has increased. You can find a 1GB EIDE hard disk for about $250 today. Combine that with the local-bus disk controller that's already on your system, and you have an excellent performance combination for a minor investment.

As you use your disk, files are constantly being created and deleted. Other files grow or shrink in size as you change them over time. Files become spread out in a patchwork-quilt pattern across the disk, making it harder for Windows to quickly find and access the one you want. To solve this problem, both DOS and Windows 95 provide a disk defragmenter (defrag). Defragment your hard disk at least once a month, even if the defrag program indicates it's not necessary. Your files may not actually be fragmented, but they may be spread out across the disk, thus increasing access times.

Since disks are considerably slower than memory, Windows uses some memory as a disk cache to increase performance. For example, Windows may read 16KB of data from disk into memory, even though a program like Word only requested 4KB of data. If Word later requests more data, Windows can deliver it from memory, rather than having to go back to disk. In Windows 3.1x, you have to set up the disk cache manually using either SmartDrive or 32-bit file access, and it's a fixed size that doesn't change in response to how you're using the system.

Windows 95 does a reasonable job of managing cache on its own, but you can tweak it to get a bit more predictable performance. In the Windows 95 SYSTEM.INI file, you can add or change the following entries:




Min and max represent the minimum and maximum KB size. Without these entries, Windows 95 uses its own defaults. My 32MB system defaults to 1,244KB (1.2MB) for min and 28,344KB (28MB) for max. The minimum is fine, but the liberal maximum setting can cause unnecessary and annoying swapping. I've found it's best to set the max to no more than one-half of your total RAM. For a 16MB system, that translates to an entry of MaxFileCache=8192.

As hard disks grow larger, the FAT file system that Windows inherited from DOS struggles to keep up. Large hard disks can mean large cluster sizes. A cluster is the amount of disk space allocated to hold files, regardless of the actual file size. Let's say you have a 1.2GB hard disk with a single partition, which means the cluster size is 32KB. If you create a 1-byte file, it will take up 32KB of disk space. A 40KB file will take up 64KB on disk. Here's a table of cluster sizes for common hard disk sizes:

Disk compression can help cure this waste of disk space in two ways. First, it will actually compress the data on disk so it takes up less space. Second, a compressed volume uses a 512-byte cluster size. As a result, it wastes very little space, even on a small file. However, disk compression has a performance penalty, because you have to compress the data with a software routine before writing it to disk. On fast systems this isn't much of a problem, but be aware of the trade-off.

One good compromise is to use Microsoft Plus Pack's DriveSpace3. It offers the option to store files in a compressed volume, but without compression. This will eliminate the waste from large cluster sizes without incurring the performance hit of compression.

If you have SCSI disks, check your MSDOS.SYS file for the line DoubleBuffer=1. This tells Windows that your disk controller requires double buffering to operate properly, which causes a major hit to performance. Sometimes this entry is erroneously placed in the file, so you might want to try commenting it out (put a semicolon in front of it) to see if you really need it.

If you find that you do need the double-buffer entry, consider getting a new controller that doesn't require that function. Also, SCSI hard disks often have their write buffer disabled by default. You will get higher performance if you enable write buffering where possible. You can usually do this by setting a jumper on the drive.

Top Tuning the CPU Tuning the Memory Tuning the Hard Disk Tuning the Video Top Tips A Clock and Bus Story Tuning the AMD Chip

Tuning the Video

Video tuning is simple. You won't encounter as many confusing possibilities as you do with other subsystems. However, there are also more situations where you need to buy hardware-not necessarily just video hardware-to solve performance problems. That's because video performance depends primarily on four items: the speed of the video board, the speed of the CPU, the bandwidth between the CPU and the video board, and the efficiency of the video driver.

The video driver software is typically the only thing you can change without an expensive hardware upgrade. Most vendors regularly provide updates to their video drivers. These updates fix bugs and sometimes add features or performance enhancements. You can look for drivers and updates at a vendor's World Wide Web site. Many vendors also have support forums on CompuServe and America Online.

One important note about video performance: When comparing video speeds, be sure to take video modes (resolution and color depth) into account. Some vendors will put most of their optimization effort into one particular driver (for example, the 1024x768 high-color driver), so you can't assume that just because a board is fast in one mode it will be fast in all of them. Wintune shows you the video mode it used for testing, so you can tell if you're comparing apples to apples. And, when you buy a system, be sure to test it in the video mode you're most likely to use.

If video performance still has you down, try using a lower color depth or resolution. On most video boards and applications, high-color 16-bit graphics are just about as good as true-color 32-bit graphics-and they are much faster. Similarly, the lower the video resolution the fewer pixels Windows has to move and the faster the response.

In Windows 95 you can change the video resolution by right-clicking on the desktop and selecting Properties from the menu, then clicking on the Settings tab. In Windows 3.1x, many vendors provide a video settings applet that you can find inside Control Panel. If yours doesn't have that option, you can change video settings by selecting Windows Setup, changing the video driver and restarting Windows.

Beyond those simple setup changes, the answer is usually to treat your system to some new hardware. See the article titled Video later in this issue.

A new generation of video graphics engines seems to appear about every six months, so better and faster boards are always on the horizon. However, the improvements are usually small and incremental. If you bought a good-quality PCI-bus video board within the last year, you aren't likely to find that the newest products are significantly faster for most desktop applications.

The new frontier for cutting-edge video performance is in multimedia functions like video playback, 3-D graphics and games. When those hit the mainstream, we'll need a whole new set of benchmarks.

Top Tuning the CPU Tuning the Memory Tuning the Hard Disk Tuning the Video Top Tips A Clock and Bus Story Tuning the AMD Chip

Top Tips

for Hot-Doggin' System Tuners


Make sure the CPU's internal cache is enabled. Watch that Turbo switch. Beware of "CPU vampires."


Install at least 8MB of RAM; 16MB is the sweet spot. Make sure external RAM cache is enabled. Put your swap file on a fast drive.


Defragment the disk regularly. For maximum speed, don't use disk compression. Set your own disk cache size.


Get the latest driver from your vendor. Don't go color crazy. Avoid true-color modes.

Top Tuning the CPU Tuning the Memory Tuning the Hard Disk Tuning the Video Top Tips A Clock and Bus Story Tuning the AMD Chip

A Clock and Bus Story

Overall performance depends on both the speed of the CPU and the speed of external memory. A fast CPU won't do much good if it's always waiting for memory to do its thing. This is especially true with the Pentium chip, which generally runs faster than the memory connected to it. For example, a 133MHz Pentium is actually fed a 66MHz clock signal, and the signal is doubled by the CPU internally to get higher speeds. The Pentium even allows noninteger multiples of the clock speed, which are used to get speeds such as 100MHz.

High clock rates on the Pentium chip can leave it waiting for results to be fetched from or written to slower external memory. To help alleviate this problem, the Pentium includes an 8KB level 1 data memory cache and a separate 8KB code cache, both of which run at full CPU speed. Outside the CPU, most Pentium motherboards also have a fast level 2 memory cache to ensure that the CPU is delayed as little as possible. This allows systems to use relatively inexpensive RAM memory SIMMs for main memory but still have very good memory performance.

This table shows the corresponding memory bus speeds for common speeds of the Pentium. The entry that really stands out is the 75MHz Pentium. It's the only one that has a slow 50MHz memory bus, which can really cripple performance. Many vendors use the 75MHz models as "value line" PCs that are devoid of level 2 memory cache, adding further insult to performance injury. If you own, or plan to buy, a 75MHz Pentium system, there may be a silver lining, however. Many motherboards that use this chip will support a faster chip, and you may be able to upgrade with a new CPU and a few jumper changes.

Pentium CPU Speed
in MHz
Memory Bus Speed
in MHz
CPU Clock Multiplier

Hard Disk
Partition Size
Cluster Size
Minimum file size
Up to 255MB4KB
Up to 511MB8KB
Up to 1023MB16KB
Up to 2048MB32KB

Top Tuning the CPU Tuning the Memory Tuning the Hard Disk Tuning the Video Top Tips A Clock and Bus Story Tuning the AMD Chip

Tuning the AMD Chip

Intel long ago turned its attention to the Pentium and recently the Pentium Pro, but other chip makers continue to deliver 486-class products with performance improvements. Two of the most popular have been the AMD Am486DX4/120 and the Am5x86/133. These chips support a write-back internal cache that improves memory accesses.

In January, a few AMD users started to visit our CompuServe and America Online discussion forums with complaints about low CPU and memory performance on desktop systems with the AMD chips. A Wintune 95 beta tester had an AMD 486/120, and we included his results in the standard database. It was clear to some other AMD users that something was amiss, because their results were far below those in the database.

The difficulty was in figuring out the root of the problem.

The problem, we discovered, was caused by incorrect jumpers on the motherboard. To take advantage of the AMD processor's improved cache, the motherboard had to be strapped for its P24D (Pentium OverDrive) setting. The settings are not intuitive at all, and the vendors who sold the AMD-based systems to these users weren't aware of this, either. After the users changed the jumpers for the P24D as documented in their system manuals, performance nearly doubled. It's just another example of how crucial the correct jumper and BIOS settings can be when you want to squeeze the most performance out of a system.

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Ahead to Upgrade It: CPU